Last year, I flew over 65,000 miles, including three cross-continental journeys, which to me, is a lot. In the process of doing so, I've established a bit of a routine in preparing for flights and long trips which has been quite helpful.
1. Bring your own food, especially if you have dietary restrictions or preferences. Nothing is worse than being rushed in a connecting flight and hungry and vegan/gluten-free/paleo. Most airplane food is carb and sugar heavy, which means that you don't feel particularly full, or particularly good afterwards. I bring those little nut butter packets, some Kind bars, some fruit, or hard boiled eggs to fill in the gaps.
2. Bring some hand sanitizer, preferably one that smells good. I have never seen the fold down tables or arm rests cleaned in an airplane, so I'm going on good faith that someone at sometime during the day cleans them...
3. Don't drink a lot of caffeine, even if you have a 6:00 AM flight. Not only will coffee make you jittery and dehydrated, it usually isn't very good on an airplane. I usually bring some teabags and ask for hot water on the plane, just so I don't end up having a Lipton Landing experience. (Or I just drink water). That way, I can have at least a fighting chance of sleeping on the plane or at my final destination.
4. If you've been feeling tired and weak, bring some emergen-c or something similar. Nothing is worse than traveling for a concert or audition and feel mid-flight that the plague has stricken you. Emergen-c might not prevent a full-out affliction, but it might delay the effects and make you a little happier for the flight. In addition, always pack a basic first aid kit-Benadryl, cold meds, Advil, etc.
5. Try to be nice and patient. Airports, much like the DMV, bring out people's unsavory sides. I often see folks snapping at flight attendants over not having their beverage of choice, and small children mowing down the elderly to get to the bathroom. Musicians tend to panic a bit about getting their instruments unboard (for good reason!), but patience, calmness, and kindness, will probably serve you better in the long run than yelling about the cost of your instrument to an airport employee who is being unhelpful.
6. Bring your music in your carry-on or case. Sometimes, you just don't want to risk having things lost.
7. When people ask if your viola/violin is a banjo/ukelele/bass, try to be nice, even if the question is absurd. The airport, much like the subway, is a fishbowl, and not everyone will be have musical knowledge. You may end up having an interesting conversation, but most likely, you'll just hear how the passenger played kazoo/sitar/euphonium in middle school. (Although I did have a family that thought my dog was a rabbit, even though they could see her chihuahua face, so...use your judgment).
8. Try not to sit in a chair in the waiting area. Your whole day will be sitting (or really, slouching) in a big chair. Stand! Sit on the floor and wake up those hips! Squat by the electrical outlets! Creating some movement pre-flight will definitely help your spine and hips to be happy. When I have a long flight, I often hide in a less popular area of the airport and stretch it out. Even better, if you're not lugging a lot of luggage or a cello, try to walk in the airport as much as time allows.
9. Keep limber on the plane! See here for thoughts beyond those weird pics in the back of the plane magazine.
10. Bring things to read. Bring earplugs for international flights. Get one of those weird neck pillows if you're on a long flight. Bring headphones, and maybe a hairbrush. (I've forgotten all of these things at some point.) Make sure your bags have your name on them. And lastly, have fun on your trip, whether it be for an audition, concerts, festivals, weddings, or family time.
Here are some more suggestions from the internet: